1. Field of the Invention
The present invention relates to a cooling system for an internal combustion engine, and more particularly to a cooling system which cools an internal combustion engine by allowing coolant to flow inside annular grooves provided on an outer surface of a cylinder.
2. Description of the Related Art
Conventionally, there is disclosed a cooling system of a cylinder liner, for example in Japanese Laid-Open Utility Model Application No. 63-168242. The cooling system disclosed in this Application, so called groove cooling, includes a plurality of grooves formed on and along an outer surface of a cylinder liner in a direction roughly perpendicular to an axis of the cylinder liner. The system also includes two connecting grooves connecting these grooves and extending in the direction of the axis of the cylinder liner. The later grooves are positioned in 180 degree opposition from each other along a diameter of the cylinder liner. Continuing passages for coolant are formed between each of the grooves on the outer surface of the cylinder liner and the inner surface of a bore of a cylinder block by fitting the cylinder liner to the bore of the cylinder block.
FIGS. 1A and 1B show an example cooling system for an internal combustion engine; FIG. 1A is a plane view and FIG. 1B is a cross sectional view taken along a line B--B of FIG. 1A. A plurality of square cross-sectioned annular grooves 3.sub.1 .about.3.sub.4 are formed on an outer surface of a cylinder liner 2. The annular grooves 3.sub.1 .about.3.sub.4, extending in a direction roughly parallel to the circumference of the cylinder liner, are equally spaced along a direction of the axis of the cylinder liner 2 that is fitted to a cylinder block 1. When the cylinder liner 2 is fitted to the bore of the cylinder block 1, these annular grooves 3.sub.1 .about.3.sub.4 form annular passages between an outer surface of the cylinder liner 2 and an inner surface 4 of a bore of the cylinder block 1.
Longitudinal grooves 5 and 6 connecting the grooves 3.sub.1 .about.3.sub.4 are formed, extending in a direction of an axis of the cylinder liner 2, in positions where the cylinder liner 2 and the cylinder block 1 face each other. In the cylinder block 1, an inlet port 7, which is connected to the longitudinal groove 5, and an outlet port 8, which is connected to the longitudinal groove 6, are formed.
A coolant delivered from a pump (not shown) is supplied to the inlet port 7. The coolant supplied to the inlet port 7 flows through the longitudinal groove 5 and is delivered to the annular grooves 3.sub.1 .about.3.sub.4. Then the coolant flows through the grooves 3.sub.1 .about.3.sub.4 while absorbing heat from the cylinder liner 2, and eventually flows into the longitudinal groove 6. The coolant flows together in the longitudinal groove 6, outflows from the outlet port 8, and is returned to the pump via a radiator (not shown).
In the system mentioned above, heat generated in a combustion chamber and transfered from a cylinder head to the cylinder liner 2 can be eliminated by cooling a wall of the cylinder liner 2. The wall of the cylinder liner 2 has an incoming heat distribution such that the incoming heat at the uppermost part of the cylinder liner 2 is highest. The amount of heat decreases toward the lower part of the cylinder liner 2. Therefore, the amount of coolant flow in the annular groove 3.sub.1 closest to a combustion chamber is maximized and the flow decreases as it flows to the grooves 3.sub.2 .about.3.sub.4 from the uppermost groove 3.sub.1, so as to uniformly cool down the wall of the cylinder liner 2.
In the conventional system mentioned above, as shown in FIG. 2, a coolant flows into the inlet port 7, and almost directly enters into the uppermost groove 3.sub.1 via the longitudinal groove 5. Some coolant flows into the grooves 3.sub.2 .about.3.sub.4, which are lower than the uppermost groove 3.sub.1. Part of the flow into grooves 3.sub.2 .about.3.sub.4 is bent perpendicularly, as indicated by arrows a and b in FIG. 2. However, since the coolant flows at high velocity, due to an inertia, it is difficult for the coolant to change a flow direction to a perpendicular direction thereof. Accordingly, in the grooves 3.sub.2 .about.3.sub.4 located below than the uppermost groove 3.sub.1, a stagnation of the coolant is generated in an upstream position of each groove as indicated by arrows c and d. This stagnation is largest at the second groove 3.sub.2 and tends to be reduced toward lower positions of the grooves. This is because the velocity of the coolant is higher at the entrance of the longitudinal groove 5 and decreases toward the downstream side due to reduced coolant flow. The result is that in inertia of the coolant flow is higher at the entrance of the second groove 3.sub.2 and lower towards the downstream position.
If stagnation of the coolant is generated at the upper portion of the cylinder liner 2, where the amount of incoming heat is considerably large, the coolant receives an excess amount of heat and begins boiling. If the vapor generated by the boiling of the coolant flows into a circulation pump for the coolant, the amount of coolant discharged from the pump will be reduced and result in an overheating of the internal combustion engine.